Riders of the Purple Sage

There is no 1912 book-club edition. The confusion is (1) later Harper states/printings that add a boxed list of Grey's earlier titles and publisher adverts to the copyright page (and later printings that eventually do carry Harper letter codes), and (2) Grosset & Dunlap and other reprint-house editions — cheaply bound, carrying their own imprint, some issued as photoplay / movie-still editions. The decisive check is the "Published January, 1912" line with no code and no title-list — not a letter code.